FR2585917A1 - METHOD FOR ADJUSTING A RADIOLOGY DEVICE - Google Patents

Abstract

THE PROCESS FOR ADJUSTING A RADIOLOGY DEVICE OF THE INVENTION INCLUDES AN INTRODUCTION PHASE 8 OF IMAGE DATA TO BE CARRIED OUT AND OF 1 XA-RAY TUBE DATA TO USE, A CALCULATION PHASE 7 OF THE TUBE ADJUSTMENT PARAMETERS AND AN ADJUSTMENT PHASE 11 OF THE PARAMETERS IN ACCORDANCE WITH THESE CALCULATIONS. AMONG THE IMAGE DATA THE NUMBER OF IMAGES TO BE MADE IS INTRODUCED, IT IS MAINLY INVOLVED IN THE OPTIMIZATION OF THE CALCULATION OF THE ADJUSTMENT PARAMETERS SO THAT THE TAKING TIME OF THE IMAGES IS AS LOW AS POSSIBLE. IN THIS WAY WE AVOID THE KINETIC BLUR.

Description

METHOD FOR ADJUSTING A DEVICE

RADIOLOGY

  The subject of the present invention is a method for adjusting a

  radiology device. This radiology device is more particu-

  most commonly of the type used in the medical field. It includes means for carrying out x-rays and / or x-rays with or without the aid of luminance amplifiers. A radiology device comprises an X-ray emitter, a patient-carrying panel, and a device for measuring the radiation produced by the tube after it has passed through a body to be examined placed on the panel. The measurement device may include a television type camera or a radiosensitive film. The handling of X-ray tubes is delicate. Their operation involves an electronic-electromagnetic transformation. Electrons emitted by a cathode strike an anode at high speed. Under

  the effect of shocks, the anode emits the expected X-radiation. However

  the transformation ratio is not worth one. Part of the energy of the incident electrons is transformed into low-frequency electromagnetic radiation: heat. It follows that

  the anode heats up and its use must be done with

  bail. Different solutions have been devised to solve this problem. In a first solution, the X-ray tubes are provided with cooling devices. In another solution

  the anode of the tubes is a rotating anode: it has the radius-

  electrons a constantly renewed surface which on average heats up less. Despite these solutions, when the load requested on the tube is too high, it is necessary to provide security. Thus, for each type of tube, a network of characteristics is measured giving, at given power and at anode temperature, the maximum duration during which the tube can be used continuously so that its anode reaches a limit temperature. This limit temperature cannot be exceeded without causing irreparable damage to the tube. Safety consists in measuring the anode temperature continuously and cutting

  tube supply when the limit temperature is reached.

  From this safe operation has been deduced a set of procedures or methods for using radiology devices. The methods, which all amount to the same thing, consist in calculating from the high tension of the tube and the dose to receive

  by a radiosensitive receiver, on the one hand, and from the temperature

  on the other hand, for how long the tube will be able to be used. Or this time of use is less than necessary and experimentation is prohibited because it cannot be completed; or this duration of use is longer than necessary and, in most cases, there is a loss of time. The anode temperature is a datum inherent to the tube at the moment when Pon wants to use it: it is calculated. High voltage and

  the dose, or sensitivity of a film, are data and images to be produced.

  The high voltage of the tube conditions the spectrum of X-rays, i.e. the penetration power of these rays6 It is determined

  by experience depending on the areas to be imaged in a human body.

  The dose, or the sensitivity of the film, is a direct consequence of this high tension and usual practices. It corresponds to the product of the heating current of the cathode of the tube by the duration during which it emits. This duration is of course the same as that of the use of the tube. This product, given in mA.s, is ultimately directly proportional to the exposure of the film. The film must have received a sufficient dose of radiation for it to be considered that it has been exposed enough. The product of high voltage, kilovolts Kv, by milliampere-seconds,

  mA.s, gives the radioelectric energy delivered by the tube, that is to say

  say, to the nearest transformation ratio, the amount of heating

that this results for the Panode.

  For example in a method, an operator displays separate-

  two radiographic data kilovolts and milliamps-

  seconds. The usage time is calculated taking into account a load chart of the tube. The drawback of this method is that if several successive exposures are made, the times of use become longer as the exposures are made. In fact, between each exposure the anode temperature has evolved by heating: its margin of evolution

  towards the limit temperature decreases. In sophis- generators

  to avoid this drawback, an operator enters a coef-

  ficient k, less than 1, which allows a microprocessor to make a calculation of exposure time with an abacus of homothetic charge than of the abacus of real charge in a factor k. In other words, the durations are not optimized. They are longer (by 1 / k). However for the examination of human bodies where certain parts are in motion, to avoid a kinetic blurring, it is necessary to choose the shortest times. As a result with this

  method if the operation is safe, it is not the best.

  The object of the present invention is to remedy the drawbacks

  cited above by simplifying the operator's work. In fact, the latter is not interested in either the temperature of the anode or the merit factor k to be attributed to an experiment. In

  the invention it suffices to indicate the number of poses N during which

  the tube should work. A microprocessor then calculates the exposure times so that they are as short as possible. The invention consists of a method for adjusting a radiology device of the type comprising the following phases: - data relating to images to be produced with the device and relating to an X-ray tube to be used are introduced into a microprocessor in the device; - we calculate with these data the tube adjustment values, and, - we adjust the tube in accordance with these values, characterized in that, - in the introduction phase we indicate, relative to the images to be produced, the desired number of these images, the high operating voltage of the tube, and the dose necessary for a radiosensitive receiver to be used to reveal the images, and that - in the calculation phase, the adjustment values are optimized in

  function of image data and tube data.

  The invention will be better understood on reading the description

  which follows and the examination of the figures which accompany it. These do not

  are given for information only and in no way limit the invention

  tion. They represent: - Figure 1: a device for implementing the method of the invention; - Figure 2: a network of parameterized curves showing the load charts of the tube:

  - Figure 3: an example of flowchart of optimization operations

  sation to be performed by a microprocessor.

  Figure I shows a device for implementing the process of the invention. It has an X-ray tube 1 which radiates 2

  a body 3. The radiation passing through the body 3 impres-

  sion, for example, a radiosensitive film 4 located in a holder

  cassette 5 placed in a patient-carrying panel 6 overhanging the body 3. A microprocessor 7 receives image data: the kilovolts determined experimentally by the nature of the body 3, the milliampere-seconds determined by the dose necessary to impress the film 4 and a number N giving the number of images

  to achieve. When the radiosensitive receiver is a film, the holder

  cassette 5 includes a film changer device for each

  image, present another film 4 under radiation 2. In radio-

  cinema or digital application, the required dose is determined

  undermined by the characteristics of the detectors used. The image data, often called radiological constants, are introduced by means of a desk 8. The microprocessor 7 also calculates the data relating to the X-ray tube: essentially the temperature cPd'anode r. In a known manner, this calculation is forecast; it takes into account the operating history of the

  tube since its commissioning. With these data the micro-

  processor 7 calculates the exposure time and the heating current for each of the N images. It comprises means, not shown, and conventional, for carrying out the adjustments of the tube. A command 10 allows an operator to commission the radiology device once the adjustments have been made. The duration of commissioning of the tube is authorized by a switch 11 which symbolizes

  the operation of the tube during its working time.

  What characterizes the invention is that, in the parameters introduced by means of the console 8, the number of images to be indicated

  perform: N. In addition, the microprocessor 7 performs an optimization

  the duration of the images to make it as short as possible.

  The operation of the process of the invention is now explained.

  that with regard to the network of curves in FIG. 2 and the organization

  gram of Figure 3. In Figure 2 the curves set in degrees (800 to 1400) indicate the maximum exposure time, for a given power of the tube and for a given initial temperature of Panode, at the end of which the temperature d the anode will reach the limit temperature. For a given power of the tube, on the ordinate Kv.mA, and for a given anode temperature, we

  can determine, on the abscissa, a maximum duration of laying envisaged

  geable. With a given power, the higher the anode temperature cP at the start of the experiment, the shorter the possible duration of use of the tube. For an image to be re-exposed or the dose, mA. s, are imposed. As high voltage is also, the product Kv. mA.s is given. This results in dashed hyperbolic traces on the network of Figure 2. Each hyperbolic trace corresponds to a given exposure. In the invention, the duration T1 obtained by the intersection of a charge diagram 12 (configured by the flow temperature of

  the anode of the tube) with a hyperbola 13 (parameterized by an expo-

  to be achieved). In the state of the art described, the presence of the factor k led in practice to retain a load chart 14 which is homothetic to the real chart 12. This resulted in the choice of a longer duration T2 and therefore unfavorable from the point of view of kinetic blurring. In a preferred example the method of the invention is implemented

  work by means of a series of operations represented diagrammatically

  only by the flowchart of figure 3. Beforehand the micro-

  processor 7 records the initial temperature e of the tube, the image data entered with the desk 8 as well as an arbitrary duration TO and an increment of arbitrary duration & T0. In one

  example To is worth 100 milliseconds and 6 To is worth 10 milliseconds.

  The microprocessor also includes in a read-only memory the tube data represented schematically by the network of load charts in FIG. 2. Firstly, in phase 15, a calculated duration of use is assimilated to the arbitrary duration: T = T0. Secondly, in a phase 16, the microprocessor calculates a walking power Pm of the tube. This walking power is equal to the ratio of the product Kv.mA.s divided by the "calculated" duration T. This walking power ultimately corresponds to a point on the curve 13. In a third phase 17 a walking time is calculated T m. This running time is obtained by transferring the running power to the load chart considered in the tube: curve 12. In FIG. 2, in the example, Tm

is less than To0.

  In a fourth phase 18 the difference between the calculated duration, here T, and the running time Tm is calculated. If this difference is greater than a precision ú. given we modify the calculated duration T in a suitable direction. In the present case T being greater than Tmn ′ it is necessary to increase the calculated duration T chosen. The duration T is replaced by T + AT. One thus proceeds on by adding (or removing) increments of arbitrary duration AT until Tm and T are sufficiently close Pun to the other. In this case each of them can be considered to be identical to the duration Ti. This duration T1 is optimum from the point of view of kinetic blurring. Indeed it is the shortest duration for which, if Pl'anode is at the start at a given temperature e, it finds itself at the end of the duration at the limit temperature. The YES output of test 18 makes it possible to adjust the cathode current: it is equal to the ratio of the last running power Pm to the high voltage Kv imposed for the tube. The unit duration Tu of each image is equal to the last calculated duration retained divided by the number of images to be taken. The high voltage of the tube remains as imposed from the start. Under these conditions, the adjustment method of the invention makes it possible to optimize

  the use of radiology devices.

Claims (3)

  1. Method for adjusting a radiology device (FIG. 1) of the type comprising the following phases: - the data relating to images to be produced (Kv, mA. S) are introduced (8) into a microprocessor (7) with the device, and relating (FIG. 2) to an X-ray tube (to) to be used in the device, - we calculate with these data values (kv, mA, T) for adjusting the tube, and, - we adjust ( 11) the tube in accordance with these values, characterized in that, - in the introduction phase, it is indicated relatively. to the images to be produced, the desired number (N) of these images, the high operating voltage (Kv) of the tube, and the dose (mA.s) necessary for a radiosensitive receiver to be used to reveal the images, and that - in the calculation phase we optimize (figure 3) the adjustment values according to the image data and data (figure 2) of the tube.   2. Method according to claim 1, characterized in that to optimize, the setting values are calculated so that the durations of   image capture correspond to the shortest possible durations.   3. Method according to claim 2, characterized in that to optimize the durations, an arbitrary duration (T0) and an equally arbitrary duration increment (îT0) are chosen, a running power (Pm) of the tube is calculated (16) relative to this arbitrary duration and to the image data (13) introduced, one calculates (17) a running time (Tm) of the tube relative to this walking power and to the data (12) of the tube, and one optimizes, by adding or withdrawal of incremental durations of arbitrary duration, the duration of walking so   that it is little different from the incremented duration.